Method and device for recording information in units

ABSTRACT

A method and device for recording information signals on a partly recorded writable record carrier ( 11 ), e.g. an optical disc. An information signal represents at least one information unit. The record carrier has a recording track which comprises preformed track position information indicative of locations for recording the information units. From the information signal a modulated signal is generated having successive frames, each frame including a synchronizing signal. The modulated signal is recorded at a one of said locations, while maintaining a fixed relationship between the track position information and the synchronizing signals. In the event that the location is after and adjacent to an already recorded location, the recording is started at a link position ( 31 ) before the end of a last frame of the earlier recorded information signal at a predefined distance before a first synchronizing signal ( 30 ) of the modulated signal.

[0001] The invention relates to a method of recording an informationsignal representing at least one information unit on a record carrierhaving a recording track which comprises preformed track positioninformation indicative of predefined locations for consecutivelyrecording the information units and a first one of said locationscomprising an earlier recorded information signal, said methodcomprising: generating from the information signal a modulated signalhaving successive frames, each frame including a synchronizing signal,and scanning said recording track and recording the modulated signal ata second one of said locations, while controlling such recording so asto maintain a fixed relationship between the track position informationand the synchronizing signals.

[0002] The invention further relates to a device for recording aninformation signal representing at least one information unit on arecord carrier having a recording track which comprises preformed trackposition information indicative of predefined locations forconsecutively recording the information units and a first one of saidlocations comprising an earlier recorded information signal, the devicecomprising modulation means for generating from the information signal amodulated signal having successive frames, each frame including asynchronizing signal, and recording means for scanning said recordingtrack and recording the modulated signal at a second one of saidlocations, and for maintaining during said recording a fixedrelationship between the track position information and thesynchronizing signals.

[0003] A method and apparatus for successively recording informationsignals on a record carrier is known from U.S. Pat. No. 5,187,699. Theinformation signal is modulated to a modulated signal having a framestructure comprising synchronizing signals for positioning the modulatedsignal in the track at predefined locations indicated by prerecordedtrack position information. The process of consecutively recordingsignals in adjacent areas in a track on the record carrier is calledlinking. In the known linking method, after a first recording signal iscompletely recorded, the recording process is continued after the lastframe of the modulated signal up to a link position. When a nextinformation signal is to be recorded, the recording process is startedat the link position by recording dummy information (usually zero data)up to the start of the following predefined location. Hence the signalprior to the first frame synchronizing signal of said following locationdoes not contain valid information. As a result a so called linkingblock is created between the first recorded signal and the secondrecorded signal, which linking block includes said link position. Hencethe linking block does not contain valid recorded information, and itsdata storage capacity is lost.

[0004] It is an object of the invention to provide a recording methodand device in which linking is more efficient.

[0005] For this purpose, the method as described in the openingparagraph is characterized in that in the event that the second one ofsaid locations is after and adjacent to the first one of said locations,the recording is started before the end of a last frame of the earlierrecorded information signal at a first predefined distance before afirst synchronizing signal of the modulated signal. Further the deviceas described in the opening paragraph is characterized in that therecording means are arranged for determining if the second one of saidlocations is after and adjacent to the first one of said locations, andin such event starting the recording before the end of a last frame ofthe earlier recorded information signal at a first predefined distancebefore a first synchronizing signal of the modulated signal. By startingthe recording within the last part of the earlier recorded signal, thesignal in the next, adjacent area, i.e. said second location, ispositioned at the nominal position and includes completely the firstsynchronizing signal as required by decoding circuits to decode the newdata recorded at the second location. Hence the modulated signal at thesecond location is completely decodable. In fact the link position islocated within the existing recorded information, and consequently themodulated signal at the first location is damaged in the very last part.Although this causes a few errors in the last symbols of the earlierrecorded information unit, this proves to be preferable to loosing anentire linking block. The errors may be acceptable for the system, or asystem of error protection may be applied to correct said errors. Themeasures according to the invention have the advantage, that no linkingblock is created and no storage capacity is lost, because the secondlocation comprising the last recorded signal is directly adjacent to thefirst location comprising the previously existing signal. In additionany recorded data stream is not interrupted by invalid data from thelinking block, which provides better compatibility with existingread-only record carriers, e.g. DVD-ROM or DVD-VIDEO.

[0006] The invention is also based on the following recognition. Usualchannel coding and decoding systems are arranged to operate on symbols(e.g. 8 or 16 channel bits). When during decoding a read signal from thelink position is decoded, the decoder will be confronted with a shift ofthe symbol boundary, a so called bit slip of a few bits, because it isin practice hardly possible to start the recording process with anaccuracy of less than one bit. As a result the decoder will detecterrors in all symbols for the full remaining part of the frame up to thenext synchronizing signal. In prior art systems this posed no problem,as the linking block did not contain useful data. However the inventorshave seen, that by selecting the linking point in the last part of theexisting frame only a few errors would arise, which further may becorrectable by modern error correcting codes.

[0007] A preferred embodiment of the device according to claim 4 has theadvantage, in the event that a new recording is to be made before andadjacent to an existing one, that the first synchronizing signal of theexisting recording is not damaged, and only a predictable and low numberof errors is generated when decoding the last recorded signal.

[0008] A preferred embodiment of the device according to claim 9 has theadvantage, that the physical starting point of recording is varied. Thishas the effect that disturbing read signal values are prevented, whilethe data is not shifted from its actual position.

[0009] A preferred embodiment of the device according to claim 10 hasthe advantage that, by using variable random data instead of a fixedpattern in said interval, the sign of the synchronizing signal is alsorandomly varied for subsequent overwrite cycles of the same location.Hence material defects in the recording layer of said location due torepeated writing of the same patterns are counteracted.

[0010] Further advantageous, preferred embodiments according to theinvention are given in the further dependent claims.

[0011] These and other aspects of the invention will be apparent fromand elucidated further with reference to the embodiments described byway of example in the following description and with reference to theaccompanying drawings, in which

[0012]FIG. 1 shows a record carrier,

[0013]FIG. 2 shows a recording device,

[0014]FIG. 3 shows the link position due to recording block N afterblock N−1,

[0015]FIG. 4 shows consecutive frames for continuous recording

[0016]FIG. 5 shows the link position for recording block N after arecorded location,

[0017]FIG. 6 shows the start position for recording block N after anunrecorded location,

[0018]FIG. 7 shows the end position for recording block N before arecorded location,

[0019]FIG. 8a shows read signal effects of overwriting at a fixedposition,

[0020]FIG. 8b shows read signal effects of overwriting at a changingposition, and

[0021]FIG. 9 shows a recording method for successively recordinginformation signals.

[0022] Corresponding elements in different Figures have identicalreference numerals.

[0023]FIG. 1a shows a disc-shaped record carrier 11 having a track 9 anda central hole 10. The track 9 is arranged in accordance with a spiralpattern of turns constituting substantially parallel tracks on aninformation layer. The record carrier may be optically readable, calledan optical disc, and has an information layer of a recordable type.Examples of a recordable disc are the CD-R and CD-RW, and writableversions of DVD, such as DVD+RW. The information is represented on theinformation layer by recording optically detectable marks along thetrack, e.g. crystalline or amorphous marks in phase change material. Thetrack 9 on the recordable type of record carrier is indicated by apre-embossed track structure provided during manufacture of the blankrecord carrier. The track structure is constituted, for example, by apregroove 14 which enables a read/write head to follow the track duringscanning. The track structure comprises position information, e.g.addresses, for iridication the location of units of information, usuallycalled blocks. The position information may include specificsynchronizing marks for locating the start of such units.

[0024]FIG. 1b is a cross-section taken along the line b-b of the recordcarrier 11 of the recordable type, in which a transparent substrate 15is provided with a recording layer 16 and a protective layer 17. Thepregroove 14 may be implemented as an indentation or an elevation, or asa material property deviating from its surroundings.

[0025] The record carrier 11 is intended for carrying informationrepresented by modulated signals comprising frames. A frame is apredefined amount of data preceded by a synchronizing signal. Usuallysuch frames also comprise error correction codes, e.g. parity words. Anexample of such a recording system is known from the DVD system, inwhich the frames carry 172 data words and 10 parity words, which exampleis used in the description below. The data is organized in unitscomprising a number of frames which contain Error Correction Codes (ECC)for correcting errors in the user information in the unit. In DVD thesize of such a unit is 32 KB user data, and contains 2 layers of errorcorrection, and is called a block. The first layer of error correction(called C1) corrects small errors like random errors, and the secondlayer (called C2) corrects the large error such as burst errors. A driveshould be able to write and/or rewrite such a block independently.According to the invention no blocks are used for linking only, allblocks are used to store user data. This means that a link positionshould be defined in order to guarantee data integrity. There willalways be some errors on a link position but the goal is to minimize theamount of errors on such a link position. The following items areimportant for the choice of the link position:

[0026] The accuracy of the writing (in channel bits) which can beachieved with respect to the data already written on the disc.

[0027] The effect of a few bit errors on the error correction.

[0028] The content of the data written on the link position.

[0029] The physical damage caused by overwriting each time the samedata.

[0030] A main consideration is, that if a bitslip occurs in combinationwith data, which is protected with error correction, then the positionof the bitslip is very important. For DVD the data is divided in to ECCunits of 32 KB, while the error correction operates on channel words orbytes. If (e.g. after the linking point) the word boundary is shiftedone or a few bits, all words are different, and no error correction cantake place. This is called bitslip. A C1 code word means one row of theerror correction and is able to detect and correct errors. A bitslip atthe beginning of a C1 code word will destroy all the bytes after thebitslip. The error correction capability is limited and the result isthat the whole C1 code word is not correctable. Now the second layer(C2) is required to correct the errors. When the bitslip occurs at theend of a C1 code word then the amount of errors is limited and the errorcorrection will be able to correct the errors. The second layer of errorcorrection is not required for the correction of errors and can be usedfor other errors. So a link position is preferable position at the endof the last C1 code word of the previous ECC unit.

[0031]FIG. 3 shows the link position due to recording block N afterblock N−1. The link position 31 is indicated by a dashed line at 32channel bits before the synchronizing signal 30, in the DVD formatcalled Sy0. For DVD the first error correction layer consists of 172data bytes and 10 parity bytes. With 10 parity bytes maximum 5 byteerrors can be corrected, but a more practical limit is less or equal to4 byte errors. The result of this insight is to position the linking ofECC block N−1 and ECC block N after the last 4 bytes of ECC block N−1and before the start of block N. The position shown at 32 channel bitscorresponds to 2 bytes (as one byte has 16 channel bits in DVD), whichgives the maximum tolerance for link position inaccuracies. In generalthe link position may be selected as close as possible before thesynchronization signal, while making sure that despite the start ofwrite link position inaccuracies in forward direction the newinformation always overwrites the old synchronization signal.Correspondingly, at the end of write before an already existinginformation unit, the new information should never damage the nextsynchronization signal of said already existing information unit. Thelast channel words of an information unit usually represent paritysymbols (called parity bytes above), and hence the minimal number ofparity symbols is damaged. In an embodiment the linking errors can belimited to errors within one symbol, when the expected link positioninaccuracies in forward and backward direction are limited to within onchannel word. The link position is then set within the last channel wordbefore the synchronizing signal, taking into account the maximal forwardand backward inaccuracies. A practical value for such a link position isthe middle of the last channel word, when a symmetrical pattern offorward and backward link position inaccuracies is expected. For achannel word of 16 channel bits this amounts to 8 channel bits beforethe end of the information unit.

[0032]FIG. 2 shows a recording device for writing information on arecord carrier 11 of a type which is (re)writable. The device isprovided with recording means for scanning the track on the recordcarrier including drive means 21 for rotating the record carrier 11, ahead 22, positioning means 25 for coarsely positioning the head 22 inthe radial direction on the track, and a control unit 20. The head 22comprises an optical system of a known type for generating a radiationbeam 24 guided through optical elements focused to a radiation spot 23on a track of the information layer of the record carrier. The radiationbeam 24 is generated by a radiation source, e.g. a laser diode. The headfurther comprises a focusing actuator for moving the focus of theradiation beam 24 along the optical axis of said beam and a trackingactuator for fine positioning of the spot 23 in a radial direction onthe center of the track. The tracking actuator may comprise coils forradially moving an optical element or may be arranged for changing theangle of a reflecting element. For writing information the radiation iscontrolled to create optically detectable marks in the recording layer.For reading the radiation reflected by the information layer is detectedby a detector of a usual type, e.g. a four-quadrant diode, in the head22 for generating a read signal and further detector signals including atracking error and a focusing error signal coupled to said tracking andfocusing actuators. The read signal is processed by a reading means of ausual type (not shown) to retrieve the information. The device comprisesmeans for processing the input information to generate a write signal todrive the head 22, which comprise an input unit 27, a formatting unit28, and a modulation unit 29. The control unit 20 controls the recordingand retrieving of information and may be arranged for receiving commandsfrom a user or from a host computer. The control unit 20 is connectedvia control lines 26, e.g. a system bus, to said means and to the drivemeans 21, and the positioning means 25. The control unit 20 comprisescontrol circuitry, for example a microprocessor, a program memory andcontrol gates, for performing the procedures and functions according tothe invention as described below with reference to FIG. 3. The controlunit 20 may also be implemented as a state machine in logic circuits.During the writing operation, marks representing the information areformed on the record carrier. The marks may be in any optically readableform, e.g. in the form of areas with a reflection coefficient differentfrom their surroundings, obtained when recording in materials such asdye, alloy or phase change material, or in the form of areas with adirection of magnetization different from their surroundings, obtainedwhen recording in magneto-optical material. Writing and reading ofinformation for recording on optical disks and usable formatting, errorcorrecting and channel coding rules are well-known in the art, e.g. fromthe CD system. The marks can be formed by means of the spot 23 generatedon the recording layer via the beam 24 of electromagnetic radiation,usually from a laser diode. User information is presented on the inputunit 27, which may comprise of compression means for input signals suchas analog audio and/or video, or digital uncompressed audio/video.Suitable compression means are described for audio in WO 98/16014-A1(PHN 16452) and for video in the MPEG2 standard. The input unit 27processes the audio and/or video to unit of information, which arepassed to the formatting unit 28 for adding control data and formattingthe data according to the recording format, e.g. by adding errorcorrection codes (ECC). For computer applications units of informationmay be interfaced to the formatting unit 28 directly. The formatted datafrom the output of the formatting unit 28 is passed to the modulationunit 29, which comprises for example a channel coder, for generating amodulated signal which drives the head 22. Further the modulation unit29 comprises synchronizing means for including synchronizing patterns inthe modulated signal. The formatted units presented to the input of themodulation unit 29 comprise address information and are written tocorresponding addressable locations on the record carrier under thecontrol of control unit 20. Usually the recording apparatus will also bearranged for reading having the reading and decoding means of a playbackapparatus and a combined write/read head.

[0033] According to the invention the control unit 20 of the recordingdevice as shown in FIG. 2 is arranged for recording the informationaccording to the methods described below with reference to the FIGS. 4to 7. The modes of writing are defined for different situations. Thestart/stop or continuous writing modes are defined separately; fourdifferent writing modes are defined: Continuous writing, Start ofwriting when the previous location is already written, Start of writingwhen the previous location is erased or not written, and End of writing.

[0034]FIG. 4 shows consecutive frames for continuous recording. Nospecial action is required. The recorder continually records from blockN−1 to block N without special action.

[0035]FIG. 5 shows the link position for recording block N after arecorded location. The link position is selected at a predefineddistance before the first synchronizing signal of the new frame. Thepredefined distance is relatively short (at least in the second half ofthe frame), but actually much closer to the end, so as to minimize thenumber of errors. For recording DVD the link position may be positionedafter byte 178 of the last C1 code word of the previous ECC unit andbefore the start of the next ECC unit, i.e. the synchronizing signalSy0. In an embodiment the data to be written before the new data startis chosen random, which is important for the interaction between old andnew data for phase change recording. Writing each time exactly the samedata over each other limits the amount of overwrite cycles. Thereforethe following measures separate or in combination may be included:

[0036] The data in the linking area can be chosen random. This willprevent overwriting each time the same data in the linking area. Anadvantage of using random data is important when the new ECC unitcontains always exactly the same data. The random data will cause alwaysof different start value of the Digital Sum Value (DSV) at the beginningof the new ECC unit. The different values of the DSV cause differencesin the following signal even when the data is not changed, and thisimproves the number of overwrite cycles of the data.

[0037] A small random shift of the link position can be introduced toimprove the direct overwrite cycles.

[0038] In FIG. 5 a distance x in error symbols (0<x<5) is indicated forthe linking distance. As discussed above the distance x must be shorterthan the number of error symbols which can be corrected. Of course theactual distance may have any value in channel bits, which results insaid number of correctable symbols, as long as the spread in thisdistance due to linking inaccuracies does not damage the nextsynchronization signal Sy0. It may be acceptable that in some cases eventhe beginning of the Sy0 synchronizing pattern is damaged, as long asthe special mark (or marks) within the synchronizing pattern, e.g. along mark I14 of runlength 14 channel bits, is not damaged, because suchspecial marks are used for detecting the synchronizing patterns.

[0039]FIG. 6 shows the start position for recording block N after anunrecorded location. When no data is written on the disc at the positionof the previous ECC block then the recording should start at least a fewhundred channel bits before the new ECC block starts. But the longer thebetter because the channel electronics (e.g. a PLL/Slicer/Syncdetection) needs time to adjust and synchronize. When at least 3 threesync frames are recorded then the flywheel construction of the sync isalready working. In this case random data is written, but the syncpatterns are of course embedded in the proper positions. In a practicalembodiment a full information unit (e.g. a full ECC block) is added asdummy unit. The dummy unit may for example be filled with random data,or may be just repeating the data of recording block N. Adding the dummyunit does not require extra settings or dedicated formatting rules inthe formatting unit 28, but only additional steps in the control unit 20for starting the writing process one information unit earlier in theevent that the recording block N is after an unrecorded area. The statusof the area N−1 before area N may be known from disc control data, e.g.a table of recorded and unrecorded areas on the disc, or detected by thedevice just before the writing of area N. Such disc control data may begenerated, stored and updated by the device itself, or by a softwaredisc operating system in controlling computer system. In an embodimentthe writing of the dummy unit on position N−1 may be started at afurther predefined and different link position, e.g. at a relativelyshort distance after the synchronization signal of unit N−1. Therebydamage inflicted upon a unit (possibly) already recorded in position N−2is prevented. For example the device moves the head to the beginning ofposition N−1 and starts reading. If no earlier recorded signal isdetected, the recording of dummy unit is started at some distance afterthe start of the area N−1. However, if an earlier recorded signal isdetected, the reading operation is continued up to said predefineddistance before the end of area N−1 and the writing is started there,i.e. at the predefined distance before the synchronization signal of thenext frame, which is the first frame of block N.

[0040]FIG. 7 shows the end position for recording block N before arecorded location. The end of writing is preferable as short as possiblebefore the position of the next ECC block, because then the errorcorrection has the minimum number of errors to correct. The remainingnumber of undamaged parity symbols x is indicated to be between 5 and 10for example for DVD, indicating that at least half the available numberis undamaged.

[0041]FIG. 8a shows read signal effects 81 of overwriting at a fixedposition, while FIG. 8b shows read signal effects 82 of overwriting at achanging position. The read signal is affected by the exact position ofthe linking in repeated overwriting. For rewritable optical discs thephase change material is very often used to record the data. A knownphenomena in phase change recording is material flow. When the start ofa recording in phase change material always starts at the same position(within a few channel bits) then large fluctuations in the signal levelwill occur after many overwrite cycles, as shown in FIG. 8A. This is nota desired situation. Some improvement can be achieved by shifting thedata randomly more than a few channel bits. But now the idea is not tostart at the same position each time but randomly vary this startposition of the recording, while the physical position of the data inthe next frame is not altered. Hence the synchronizing signal is locatedat its nominal position. For example: The first recording starts at bytenumber 180 of the last C1 code word of the previous ECC unit and willwrite 2 bytes before the first C1 code word of the next ECC unit starts.The second recording (at that same location) starts at byte number 178of the last C1 code word of the previous ECC unit and writes 4 bytesbefore the first C1 code word of the next ECC unit starts. The result isa variable start position of the recording while the position of thefurther data is not changed. The random variation may be selected tohave any number of channel bits. The maximum and minimum distance shouldresult in an amount of errors within the error correction capability. Apractical implementation is a random selection between a minimum and amaximum distance.

[0042]FIG. 9 shows a recording method for successively recordinginformation signals. It is assumed that a record carrier of a writabletype is inserted in a recording device and that it already contains somerecorded information. In a first step 91 (COMMAND) a command is receivedto record block N. In a second step 92 (SCAN) the track on the recordcarrier is scanned up to the preceding location of block N−1. In a firsttest 93 it is decided, if the preceding location is not blank (i.e.contains already some information signal). If NOT BLANK, in a step 95 astart position is determined at a first predetermined distance asdescribed above with reference to FIG. 5. If no information signal ispresent on the preceding location, in a step 94 a long sequence of dummydata is recorded before the start of location N to enable any readcircuit to lock to the data as described with reference to FIG. 6. Instep 96 after said steps 94 or 95 the actual block N (or severalcontinuous blocks as described with reference to FIG. 4) are recorded.In test 97 the status of the location N+1 after block N is determined.This may be accomplished by scanning the track before the recording isstarted, e.g. in step 92. Alternatively a special table may be presenton the record carrier or in the device which keeps track of unrecordedand recorded areas, e.g. in the file management system. In the eventthat no signal is recorded after block N (or the signal has no validstatus, e.g. erased), in a step the recording process is continued atleast until the modulated signal of block N is completely recorded, andit may be continued for some predetermined distance after the last frameto prevent any read circuit from detecting a read error prematurely. Inthe event that the next location N+1 contains a valid informationsignal, in a step 99 the recording process is stopped at a secondpredetermined distance before the modulated signal of block N iscompletely recorded as described with reference to FIG. 7. After steps98 or 99 the recording of block N is completed, and a next command maybe awaited.

[0043] In an embodiment the test 97 is omitted and the recording processis always stopped at a short predetermined distance before the nominalposition of the start of the synchronizing signal of the next block. Inaddition the above embodiments may be arranged to select the secondpredetermined distance always shorter than the first predetermineddistance. This has the advantageous effect, that no unrecorded gaps willexist between successively recorded blocks. It is to be noted thatstarting and ending point inaccuracies must be taken into account.

[0044] Although the invention has been explained by embodiments usingthe DVD-optical recording format, it may be applied for any format forrecording units of information. For example the record carrier may alsobe a magnetic type disc or a tape. It is noted, that in this documentthe word ‘comprising’ does not exclude the presence of other elements orsteps than those listed and the word ‘a’ or ‘an’ preceding an elementdoes not exclude the presence of a plurality of such elements, that anyreference signs do not limit the scope of the claims, that the inventionmay be implemented by means of both hardware and software, and thatseveral ‘means’ may be represented by the same item of hardware.Further, the scope of the invention is not limited to the embodiments,and the invention lies in each and every novel feature or combination offeatures described above.

1. Method of recording an information signal representing at least oneinformation unit on a record carrier having a recording track whichcomprises preformed track position information indicative of predefinedlocations for consecutively recording the information units and a firstone of said locations comprising an earlier recorded information signal,said method comprising: (a) generating from the information signal amodulated signal having successive frames, each frame including asynchronizing signal, and (b) scanning said recording track andrecording the modulated signal at a second one of said locations, whilecontrolling such recording so as to maintain a fixed relationshipbetween the track position information and the synchronizing signals,and characterized in that (c) in the event that the second one of saidlocations is after and adjacent to the first one of said locations, therecording is started before the end of a last frame of the earlierrecorded information signal at a first predefined distance before afirst synchronizing signal of the modulated signal.
 2. Method as claimedin claim 1, wherein the recording is terminated before the modulatedsignal is completely recorded at a second predefined distance before anominal position of a first synchronizing signal of an informationsignal at the subsequent one of said locations.
 3. Device for recordingan information signal representing at least one information unit on arecord carrier (11) having a recording track (9) which comprisespreformed track position information indicative of predefined locationsfor consecutively recording the information units and a first one ofsaid locations comprising an earlier recorded information signal, thedevice comprising modulation means (29) for generating from theinformation signal a modulated signal having successive frames, eachframe including a synchronizing signal, and recording means(20,21,22,25) for scanning said recording track and recording themodulated signal at a second one of said locations, and for maintainingduring said recording a fixed relationship between the track positioninformation and the synchronizing signals, characterized in that therecording means (20,21,22,25) are arranged for determining if the secondone of said locations is after and adjacent to the first one of saidlocations, and in such event starting the recording before the end of alast frame of the earlier recorded information signal at a firstpredefined distance before a first synchronizing signal of the modulatedsignal.
 4. Device as claimed in claim 3, wherein the recording means(20,21,22,25) are arranged for terminating the recording before themodulated signal is completely recorded at a second predefined distancebefore a nominal position of a first synchronizing signal of aninformation signal at the subsequent one of said locations.
 5. Device asclaimed in claim 3 or 4, wherein the device comprises error coding means(28) for including error codes in the modulated signal, and said firstor second predefined distance is smaller than a distance over whicherrors are correctable on the basis of the error codes.
 6. Device asclaimed in claim 5, wherein the error coding means (28) are arranged forincluding at least two layers of error codes, and said first or secondpredefined distance is smaller than a distance over which errors arecorrectable on the basis of the error codes of the first layer. 7.Device as claimed in claim 5, wherein the modulated signal compriseschannel words representing the error codes and the information signal,and said first or second predefined distance substantially correspondsto half the length of a channel word.
 8. Device as claimed in claim 4,wherein the second predefined distance is smaller than the firstpredefined distance.
 9. Device as claimed in claim 3, wherein therecording means (20,21,22,25) are arranged for variably selecting thefirst predefined distance between a minimum and a maximum value, whilemaintaining the position of the first synchronizing signal.
 10. Deviceas claimed in claim 3, wherein the recording means (20,21,22,25) arearranged for recording variable random data in the interval between thepredetermined distance and the first synchronizing signal.
 11. Device asclaimed in claim 3, wherein the recording means (20,21,22,25) arearranged for, in the event that the second one of said locations isafter and adjacent to an unrecorded area, starting the recording at athird defined distance substantially larger the first predefineddistance.
 12. Device as claimed in claim 11, wherein the thirdpredefined distance is substantially equal to the length of aninformation unit.
 13. Device as claimed in claim 3, wherein the devicecomprises means (27) for processing or compressing digital or analoginput signals such as audio and/or video to units of information.